The correct answer is: A. Anaerobic decomposition.
Anaerobic decomposition is a type of decomposition that occurs in the absence of oxygen. This type of decomposition is typically slower than aerobic decomposition, but it can still be effective in breaking down organic matter. In septic tanks, anaerobic decomposition is used to treat sewage. The sewage is broken down by bacteria that do not require oxygen to survive. This process produces methane gas, which is released into the atmosphere.
Aerobic decomposition is a type of decomposition that occurs in the presence of oxygen. This type of decomposition is typically faster than anaerobic decomposition, and it produces less methane gas. Aerobic decomposition is used in some sewage treatment plants to treat sewage. The sewage is broken down by bacteria that require oxygen to survive. This process produces carbon dioxide gas, which is released into the atmosphere.
Parasitic decomposition is a type of decomposition that occurs when parasites break down organic matter. This type of decomposition is typically not used in sewage treatment. Parasites can cause disease, so they are not typically used in processes that involve human waste.
In conclusion, the correct answer is: A. Anaerobic decomposition.